This invention concerns polymeric binders which are suitable for use in ink jet inks. More specifically, this invention relates to polymeric binders formed by polymerization of a monomer mixture comprising a polymerizable surfactant monomer.
Certain ink jet inks comprise a liquid medium, a colorant, such as a pigment or dye, a binder or resin to aid in dispersing the pigment in the medium and to affix the colorant to the print surface. In order to create more durable print quality, particularly in terms of color-fastness and water- and rub-resistance of the printing ink, there has been interest in preparing ink jet inks in which the colorant is an insoluble pigment, rather than a water soluble dye. The latter are generally absorbed to some degree by the paper or other print medium, but due to their inherent water-solubility do not offer good waterfastness. Pigment-based inks are generally deposited on the surface of the print medium, making them susceptible to removal by water or abrasion. However, as a result of the physical properties of pigments, pigment based ink compositions have a tendency to have a low wet-rub resistance and low highlighter resistance.
The term xe2x80x9cwet-rub,xe2x80x9d as used herein, means applying abrasive pressure across the printed substrate with a wetted paper facial tissue and measuring any smear created thereby; wet-rub differs from waterfastness because abrasion is used. The term xe2x80x9chighlighter resistance,xe2x80x9d as used herein, means applying abrasive pressure across a printed substrate with a commercially available highlighting marker and measuring any smear created thereby; an example of such marker is Sanford Corp. Major Accent brand highlighting markers. The term xe2x80x9cprint qualityxe2x80x9d, as used herein, means an accumulative evaluation of the overall performance of an ink jet ink as measured by the appearance of a printed page of combined text and graphics, including edge sharpness, bleed, feathering, optical density, wet-rub resistance, highlighter resistance and print operability. The term xe2x80x9cprint operabilityxe2x80x9d, as used herein, means an accumulative evaluation of printer performance, including print appearance and uniformity, page after page longevity of print quality and uniformity, nozzle drop outs, print head maintenance problems, and the ability to stop and restart printing.
Polymer binders have been added to ink jet ink compositions to improve durability, to improve print quality and to reduce color bleeding and feathering. However, the inclusion of such binders can result in increased printhead maintenance problems, including clogging of the nozzles and kogation, i.e. formation of film on or about the heater. Also, polymers may tend to form films on the nozzle plate. The addition of polymers to ink jet ink compositions also may cause decreased pigment dispersion stability and interference with bubble formation.
EP-A-0869 160 discloses an inkjet ink formulation with colorant, vehicle and resin emulsion containing ionic carboxylic groups on the surface of resin emulsion particles to cause disassociation of the colorant and resin particles. The resin has 1 to 40 wt. % xe2x80x9ccarboxylic acid groupsxe2x80x9d, and Tg of 0 to 120xc2x0 C. Exemplified embodiments of the resin include copolymers of butyl acrylate, methyl methacrylate and (meth)acrylic acid, with 3 to 20 wt. % acid, Tg of 53 to 95xc2x0 C. and particle size of 63 to 235 nm, utilizing high Tgs and low particle sizes.
EP-A-0747456 discloses a method for providing a waterborne coating composition, such as a paint, having improved color acceptance. The coating composition contains an emulsion-polymerized addition polymer formed from a mixture of monomers including a polymerizable surfactant monomer. There is no disclosure of the use of the addition polymer in an ink.
It is an object of the present invention to provide a polymeric binder for use with a colorant to form an ink jet ink that demonstrates an improved print quality, as expressed by an improvement in one or more properties used to determine print quality, which improvement is achieved without any significant detrimental effect on the other properties used to determine print quality.
In accordance with the present invention, there is provided a polymeric binder suitable for use in an ink composition, preferably an ink jet ink composition, comprising a colorant and a polymeric binder, wherein the polymeric binder is an emulsion-polymerized addition copolymer formed from a monomer mixture comprising ethylenically unsaturated monomers including from more than 4 to 15 wt % based on the weight of said mixture of at least one ethylenically unsaturated carboxylic acid functional monomer, and from 0.05 to 5 wt % based on the weight of said mixture of at least one polymerizable surfactant monomer comprising hydrophobic and hydrophilic functional groups, wherein said hydrophobic functional group comprises a polymerizable group within it.
In another aspect, there is provided an ink composition, preferably an ink jet composition, comprising a colorant and a polymeric binder, wherein the polymeric binder is an emulsion-polymerized addition copolymer formed from a monomer mixture comprising ethylenically unsaturated monomers including from more than 4 to 15 wt % based on the weight of said mixture of at least one ethylenically unsaturated carboxylic acid functional monomer, and from 0.05 to 5 wt % based on the weight of said mixture of at least one polymerizable surfactant monomer comprising hydrophobic and hydrophilic functional groups, wherein said hydrophobic functional group comprises a polymerizable group within it.
In yet another aspect of the present invention, there is provided the use of an emulsion-polymerized addition copolymer, formed from a monomer mixture comprising ethylenically unsaturated monomers including from more than 4 to 15 wt % based on the weight of said mixture of at least one ethylenically unsaturated carboxylic acid functional monomer and from 0.05 to 5 wt % based on the weight of said mixture of at least one polymerizable surfactant monomer comprising hydrophobic and hydrophilic functional groups, wherein said hydrophobic functional group comprises a polymerizable group within it, as a polymeric binder in an ink composition, preferably an ink jet composition, to improve the print quality of said ink composition.
Surprisingly, ink jet inks comprising a binder of the present invention demonstrate improved print quality over binders of similar composition but which do not comprise a polymerized surfactant monomer. In addition, ink jet inks of the present invention may demonstrate an improved optical density.
Polymerizable surfactant monomers are known in the art. They are surface active compounds having a polymerizable group, such as an allyl, acryl, methallyl or methacryl group (herein also referred to as (meth)acryl or (meth)allyl group), and which may be used as an emulsifier in an emulsion polymerization. Thus, the polymerizable surfactant functions as both a surfactant and as a comonomer. The polymerizable surfactant may be cationic, anionic or nonionic. Suitable polymerizable surfactant monomers comprising hydrophobic and hydrophilic functional groups, wherein said hydrophobicfunctional group comprises a polymerizable group within it include, for example, anionic surfactant monomers such as sulphates, phosphates, sulphosuccinate half esters, and sulphosuccinate diesters bearing copolymerizable reactive groups and nonionic surfactant monomers such as nonylphenoxy propenyl polyethoxylated alcohols (for example as Noigen RN-20 from Dai-ichi Corp). Preferred polymerizable surfactant monomers are nonylphenoxy propenyl polyethoxylated sulphate (for example as Hitenol from Dai-ichi Corp); sodium alkyl allyl sulphosuccinate (for example as Trem LF-40 from Henkel Corp); ammonium di-(tricyclo(5.2.1.0 2,6) dec-3-en-(8 or 9)oxyethyl) sulfosuccinate; and ammonium di-(tricyclo(5.2.1.0 2,6) dec-3-en-(8 or 9) sulfosuccinate. Additionally, the ammonium and metal salts of unsaturated C6 to C30 organic acids may be suitable, these may be used alone or in combination with the above surfactants. Examples of these acids are: alpha methyl cinnamic acid, alpha phenyl cinnamic acid, oleic acid, lineolic acid (as described in U.S. Pat. No. 5,362,832), rincinoleic acid, the unsaturated fraction of Tall oil rosin and fatty acids, disproportionated rosin acid, soybean oil fatty acids, olive oil fatty acids, sunflower oil fatty acids, linseed oil fatty acids, safflower oil fatty acids, sorbitan mono-oleate, abietic acid, poly(oxyethylene) sorbitol sesquioleate, and Empol 1010 Dimer Acid. Suitable polymerizable surfactant monomers also include, for example, maleate derivatives (as described in U.S. Pat. No. 4,246,387), and allyl derivatives of alkyl phenol ethoxylates (as described in JP-62227435).
The amount of polymerizable surfactant monomer in the monomer mix is preferably from 0.075 to 2 wt %, more preferably 0.075 to 0.5 wt %, based on the weight of said mixture.
The ethylenically unsaturated carboxylic acid functional monomers are preferably C3 to C20 ethylenically unsaturated carboxylic acids, more preferably monomers selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid and anhydrides of such acids; their basic salts e.g. the ammonium, quaternary alkyl ammonium, lithium, sodium and potassium salts thereof; and mixtures of such monomers. Alternatively, the ethylenically unsaturated carboxylic acid monomer may be an oligomer of acrylic or methacrylic acid, preferably having a molecular weight of no more than 5000 Daltons.
The amount of ethylenically unsaturated carboxylic acid monomer in the monomer mix is preferably from more than 4 to 10 wt %, more preferably from 4.5 to 9 wt %, based on the weight of said mixture.
Other ethylenically unsaturated monomers suitable for use in said monomer mix include one or more monomers selected from, but not limited to: substituted e.g. hydroxy- or acetoacetoxy-substituted and unsubstituted (C1 to C50, preferably C1-C22, most preferably C1 to C18) alkyl (meth) acrylates, styrene and substituted styrenes, vinyl acrylates, vinyl acetates, fluoromethacrylates, acrylamide, substituted acrylamides, methacrylamides, substituted methacrylamides, and combinations thereof Among the esters of acrylic acid and methacrylic acid, preferred monomers include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, ethylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, lauryl methacrylate, isobutylene methacrylate, hydroxyethyl (meth)acrylate and acetoacetoxy (meth)acrylate. Most preferably, the monomers are selected from the group consisting of methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, ethylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, lauryl methacrylate, isobutylene methacrylate, styrene, acrylamide, vinyl acrylate, vinyl acetate, hydroxyethyl acrylate and hydroxyethyl methacrylate.
In one embodiment, the binder comprises an addition copolymer of ethylhexyl acrylate, methyl methacrylate, methacrylic acid and sodium alkyl allyl sulphosuccinate.
Preferably the binder comprises an addition polymer with a glass transition temperature, Tg, of at least xe2x88x9240xc2x0 C., more preferably in the range from xe2x88x9235 to about 120xc2x0 C., yet more preferably in the range from xe2x88x9235 to 20xc2x0 C., and even more preferably in the range from xe2x88x9230 to 10xc2x0 C. Tg can be determined by the Fox equation.
In a preferred embodiment, the polymer binder comprises a single stage addition polymer with an average diameter in the range from about 100 to 400 nm. More preferably, the average diameter is in the range 200 to 350 nm. The average particle diameter may be determined by a light scattering technique, such as by employing a Brookhaven Instruments Corporation, xe2x80x9cBI-90 Particle Sizerxe2x80x9d analyzer.
The particle size distribution of the binder polymer may be unimodal, bimodal or polymodal, but modality is not considered important to the practice of this invention.
The molecular weight of the polymeric binder is not critical. However, it has been found that the binder polymers preferably has a molecular weight in the range from about 10,000 to about 2,000,000 Daltons; more preferably, 50,000 to 1,000,000 Daltons. The molecular weight as used herein is defined as the weight average molecular weight and may be determined by gel permeation chromatography in THF as solvent.
The ink composition of the present invention may further comprise additional components including without limitation process aids such as other (free) surfactants, protective colloids, and other stabilizers known to those skilled in the art. Suitable surfactants, for example, include sodium lauryl sulfate, sodium dodecylbenzene sulfonate, sodium dioctyl sulfosuccinate, and ammonium perfluroralkyl sulfonates, Triton X-100, Triton X-405, and polyoxyethylenated polyoxypropylene glycols.
The addition polymer may be prepared by a conventional persulfate-initiated thermal process known in the art such as batch, semi-batch, gradual addition or continuous, for example as described in EP-A-0747456. The monomers are polymerized to preferably greater than 99% conversion and then the reaction is cooled to room temperature (20-25xc2x0 C.) after the addition of the appropriate amount of neutralizing base to control pH. The pH is adjusted to between pH 7-10, more preferably between pH 8-9, with neutralizer such as, for example, ammonia, lithium hydroxide, sodium hydroxide, potassium hydroxide or combinations of these neutralizers.
The binder may be incorporated in an ink composition, preferably an ink jet ink composition, comprising, for example, pigment, binder and an aqueous medium. Preferably, the binder is present at a level of 0.1 to 10 weight percent, preferably, 0.5 to 8 weight percent, more preferably 1 to 5 weight percent relative to the total weight of the ink composition. The aqueous carrier may be water; preferably, deionized water. In one embodiment, the aqueous carrier is present at from about 40% to about 95%, preferably from about 55% to about 80%, most preferably, from about 70% to about 80% by weight of the ink composition. Selection of a suitable mixture for the ink composition using the binder of the present invention depends upon the requirements of the specific ink being formulated, such as the desired surface tension and viscosity, the pigment used, the drying time required for the pigmented ink and the type of paper onto which the ink will be printed.
The ink composition using the binder of the present invention may also include water miscible materials such as humectants, dispersants, penetrants, chelating agents, co-solvents, defoamers, buffers, biocides, fungicides, viscosity modifiers, bactericides, surfactants, anti-curling agents, anti-bleed agents and surface tension modifiers, all as is known in the art. Useful humectants include ethylene glycol, 1,3 propanediol, 1,4 butanediol, 1,4 cyclohexanedimethanol, 1,5 pentanediol, 1,6 hexanediol, 1,8 octanediol, 1,2 propanediol, 1,2 butanediol, 1,3 butanediol, 2,3 butanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol with average molecular weight of 200, 300, 400, 600, 900, 1000, 1500 and 2000, dipropylene glycol, polyproylene glycol with average molecular weight of 425, 725, 1000, and 2000, 2-pyrrolidone, 1-methyl-2-pyrrolidone, 1-methyl-2-piperidone, N-ethylacetamide, N-methlpropionamide, N-acetyl ethanolamine, N-methylacetamide, formamide, 3-amino-1,2-propanediol, 2,2-thiodiethanol, 3,3-thiodipropanol, tetramethylene sulfone, butadiene sulfone, ethylene carbonate, butyrolacetone, tetrahydrofurfuryl alcohol, glycerol, 1,2,4-butenetriol, trimethylpropane, pantothenol, Liponic EG-1. Preferred humectants are polyethylene glycol with average molecular weight of 400 to 1000, 2-pyrrolidone 2,2 thiodiethanol, and 1,5 pentanediol. Preferred penetrants include n-propanol, isopropyl alcohol, 1,2 hexanediol, and hexyl carbitol.
Examples of colorants useful in the method of the present invention are selected from the group of pigments and dyes generally useful in ink jet printing. Suitable organic pigments include carbon black, azo compounds, phthalocyanine pigments, quinacridone pigments, anthraquinone pigments, dioxazine pigments, indigo, thioindigo pigments, perynone pigments, perylene pigments, and isoindolene. Suitable inorganic pigments include titanium dioxide, iron oxide, and other metal powders. The amount of pigment is generally determined by the desired properties of the ink to be made. Generally, the amount of pigments used is less that 10% and is typically from 3-8% by weight based on the total weight of all the components of the ink. The pigment particle size must be sufficiently small that pigment particles will not clog the nozzles on the printing device in which the ink is to be used. Typical nozzle openings on thermal ink jet printers are 30-60 microns in diameter. Preferably, the pigment particle size is from 0.05 to 2 microns, more preferably not more than one micron and most preferably not more than 0.3 microns.
The amount of humectant used is determined by the properties of the ink and may range from 1-30%, preferably from 5-15% by weight, based on the total weight of all the components in the ink. Examples of commonly used humectants useful in forming the ink are: glycols, polyethylene glycols, glycerol, ethanolamine, diethanolamine, alcohols, and pyrrolidones. Other humectants known in the art may be used as well.
The use of suitable penetrants will depend on the specific application of the ink. Useful examples include pyrrolidone, and N-methyl-2-pyrrolidone.
The amount of defoaming agent in the ink, if used, will typically range from 0.05-0.5% by weight, and is more typically 0.1 wt. %. The amount required depends on the process used in making the pigment dispersion component of the ink. Defoaming agents useful in forming aqueous dispersions of pigments are well known in the art and commercially available examples include Surfynol 104H and Surfynol DF-37 (Air Products, Allentown, Pa.).
The remaining portion of the ink is generally water. The amount of water preferably is from 65-90% by weight, more preferably from 75-85% by weight, based on the total weight of all the components in the ink.
The ink compositions of the present invention may be prepared by any method known in the art for making such compositions, for example, by mixing, stirring or agitating the ingredients together using any art recognized technique to form an aqueous ink. The procedure for preparation of the ink composition of the present invention is not critical except to the extent that the ink composition is homogenous.
One method for preparation is as follows: Mix the aqueous carrier, humectant(s), surfactant(s) and penetrant(s) for 10 minutes, or until homogenous. Prepare pigment-dispersant mixture by milling a 5 to 1 ratio of pigment to dispersant to a total of 20% solids in water. Slowly add aqueous carrier/humectant/surfactant/penetrant solution to pigment-dispersant while pigment(s) remains stirring. Let stir for another 10 minutes, or until homogeneous. Slowly add the pigment dispersion/carrier/humectant/surfactant to the polymeric binder with stirring. Continue to stir for 10 minutes or until homogenous. Adjust pH of the resultant ink to 8.2-8.5 (e.g. by adding sufficient 20% NH4OH). Filter through a 1 micrometer filter. It is expected that the ink compositions using the binders of the present invention would include any additives necessary to obtain the desired physical properties required for the end use of the ink composition such additives include chelating agents, buffers, biocides, fungicides, antioxidants, rheology modifiers, thickeners, bacteriocides, surfactants, anti-curling agents, anti-bleed agents and surface tension modifiers, all as discussed above.
The invention in some of its embodiments will now be further described by reference to the following examples: